Dual wave band radioreceiver



May 29, 1934. L. F. CURTIS ET AL DUAL WAVE BAND RADIORECEIVER Filed Oct.28, 1931 2 Sheets-Sheet l OQOOOOOOOOOOOOOQCOO INVENTORS leslie I-TCari/5.

William E Cotter. leopard .a5iman Q2 z nsmlva May 29, 11934. L. F.CURTIS ET AL DUAL WAVE BAND RADIORECEIVER lFiled Oct. 28, 1951 2Sheets-Sheet f2 INVENTORS 19511: F. (a/as.

P/z'lh'am E Cotter: leonard Eastman- QQEfl Patented May 29, 1934 UNITEDSTATES PATENT FFHIE DUAL WAVE BAND RADIORECEIVER Leslie F. Curtis,William F. Cotter, and Leonard E. Eastman, Springfield, Mass, assignorsto United American Bosch Corporation,

Springfield,

4 Claims.

Our invention relates to improvements in receivers; and especially toreceivers for use in broadcasting and other forms of radiocommunication.

An object of the invention is to provide a radio receiver of such designthat it will operate on at least two distinct and predetermined bands ofwave lengths or frequencies, so that the receiver can readily beutilized in different localities where separate bands are necessary fortransmission; or in one locality to operate on either band, as the usermay wish.

A further object of our invention is to provide a radio receiver whichhas means for enabling it to receive on one band or another; and whichis built to contain for this purpose suitable electrical devices whichcan be manipulated to adjust the receiver according to the band on whichreception is to be accomplished.

Another object of the invention is to provide a radio receiver which isequipped with one or more coils in separate sections, all of which maybe connected in circuit for the band of longer wave lengths; or onlypart of which may be actively employed when reception on shorter wavelengths is required.

A still further object of the invention is to provide a convenientarrangement of the coils by which long or short wave reception can beeffected; together with suitable members in the form of switches orsimilar parts by which the coils can easily be controlled in unison; sothat the change in adjustment necessary to shift from one band to theother can be quickly brought about.

In practice, the receiver is designed to work upon a band of wavelengthshaving a range of say 200 to 600 meters; and it has an additional set ofwindings to afford a greater inductance and adapt the receiver to be setfor the other band, which lies between 1000 and 2000 meters; togetherwith regulating switches to include or out out the additional windingsat will; these switches being arranged and joined in tandem, so that allof them can be actuated at one time.

An additional object of the invention is to provide a radio receiverhaving novel resistance-repeating cascade-connected amplifier circuitsdesigned to aiford excellent control of the gain or amplification ineach stage, and ease of obtaining wave length range.

The objects and advantages of the invention are fully set forth in theensuing description, taken with the accompanying drawings which show thepreferred form of the invention. The

disclosure, however, is explanatory only and variations in theconnections and other relations of the various elements and appliancesincluded in our improved receiver, may be adopted without departing fromthe principle of the invention or exceeding the scope of the appendedclaims.

On the drawings:

Figure 1 shows a circuit for a receiver according to our invention;

Figure 2 is an end view of the regulating or adjusting devices orswitches to set the receiver for the separated bands of Wavelengths orfrequcncies, and means for actuating the same; some of the covering andmounting parts being in section;

Figure 3 is a front view of said devices; and

Figures 4 and 5 present charts to explain the mode of operation of therepeating circuits.

The same numerals identify the same parts throughout.

As illustrated the receiver comprises electric circuits containingvacuum tubes for radio frequency amplification in cascade, together witha suitable detector and at least one stage of audio frequencyamplification; all disposed to operate on the resistance-repeatingprinciple, and to give suitable amplification on both bands; tunedcircuits for selectivity; and a rectifier with asso ciated means tosupply current from ordinary lighting or power mains; so that batteriescan be dispensed with as sources of electrical energy for the cathodesand anodes of the tubes or thermionic valves. It is to be understood,however, that our invention is to be by no means limited to such areceiver but be embodied in receivers of various constructions.

Referring particularly to the drawings, we show a terminal 1 for anantenna at one end of a resistance 2, with which is associated anadjustable contact 3 connected to ground The terminal 1 is alsoconnected to one terminal of an adjustable electrical condenser 5, theother pole of which is joined to the grid of the first vacuum tubemember or amplifier 6. The terminal of the resistance 2 remote from thecondenser 5 is united through a suitable resistance 7 to the cathode inthe tube 6, this tube being or" the screen-grid type, the cathode beingof the unipotential type and grounded as shown through a fixed condenser8. The shield or screen in the tube 6 is grounded in the same way.Attached to the lead between the grid of the tube 6 and condenser 5 is acoil including a pair of sections 9 and 10, these sections being inseries and grounded. They are also associated with an adjustablecondenser 11 connected to the grid of the tube 6 at one end and groundedat the other. The sections 9 and 10 and condenser 11 constitute a tuningcircuit and the tube 6 as shown is joined to the antenna by a resistancecoupling because of the presence or the element 2. When the receiver isto be used for waves of the longer length, both sections 9 and 10together with the condenser 11 are put into circuit. When, however, theband of shorter wave lengths is to be employed, section 10 can be cutout by bridging the terminals 12 connected to the two ends of thesection 19 by suitable switch mechanism. Obviously more than twosections may be utilized if operation on more than two bands ofwavelengths is desired.

The second radio-frequency amplier tube (in is of the same descriptionas the first tube 6 and is connected to the first tube by a conductorextending between the plate of the first tube and the grid of thesecond, with a fixed condenser 5a in line thereof. Similar connectionsare pro vided for the filament of tube 6a extending from the terminal ofthe resistance 7 and including a condenser 8a joined to ground asbefore; with another condenser 8a to ground the screen between the anodeand grid. Between the con denser 5a and the grid of the tube 6a is atuned circuit consisting again of a coil in two sections 9a and 10a inseries and grounded, together with an adjustable grounded condenser 11aconnected to the grid of tube 6a; the section 10a having contacts 12ajoined to its extremities, so that this coil can be switched out at thesame time as the coil 10.

Between the condenser 50', and the plate of the first tube 6 is joinedone end of the resistance 2a which is of high value and across which theplate circuit load is developed; this high resistance 2a havingcapacity-coupling through the condenser 5a with the tuned circuitcomprising coils 9a and 10a and condenser 11a. Similar coupling existsbetween the first resistance 2 and the first tuning circuit of the tube6.

The same connections exist between the plate of the tube 6a and the gridof the radio frequency detector tube 62); the corresponding repeatingresistance being shown at 22), tuning coil section at 91) and 10b,tuning condenser at 11b, switching contacts at 121) and couplingcondenser at 5?). Associated with the tuning circuits of the tubes (isand 6b are suitable adjustable trimming condensers lla and 111) whichare grounded the same as the condensers 11a and 11b. Suitable condensers8 and 3" ground one terminal or the resistances 2a and 2b. We alsoconnect the filament of the detector tube 6b to one end of a resistance7b and condenser 81) in parallel, the opposite terminals of these twoelements being grounded on the framework of the receiver.

The condensers 8, 8a, 8 and 8 are by-pass condensers for high frequencyoscillations; while the condensers 8b attached to the screen and thecathode of the tube 6b constitute by passes for both radio and audiofrequency oscillations. The resistance 72) of the detector cathode isfor grid bias purposes.

The last stage in the circuits of the receiver comprises an audiofrequency amplifier 6c having a capacity coupling through a condenser 50with the plate of the detector tube 612. To the lead between thiscondenser and the plate of the tube 62) is united one end of aresistance 20; and joined to the conductor of this plate between theresistance 20 and the tube 62) is a ground detector plate condenser 110for rectification. The screens of the tubes 6, 6a and 6b are connectedthrough leads 13, 13a and 13b to a common terminal 14; and a suitableresistance 7b may be inserted in the lead 131).

Joined to the grid of the tube 60 and between the tube and the condenser50 are two coupling resistances 15 and 16 in series, between which isone pole of a condenser 1'7; the other pole 01 which is grounded andconnected to a pair of coils 18 bridged across the filament of the audioamplifier tube 60. The resistance 15 and condenser 17 are in a circuitbetween grid and filament for audio frequency current, and are connectedto the mid-point of the windings 18 to allow for alternating currentfluctuations of the heating current. The plate of the tube 60 isconnected to one terminal of the primary coil 19 of an iron coretransformer, the secondary 20 of which is to have its terminalsconnected to the movable coil of the dynamic loud speaker.

To supply current to the plates of the tubes the resistances 2a and 2band 2c are joined to a common conductor 21 which is grounded at one endand connected at the other to the heated cathode of a rectifier 22. Thisrectifier also contains two anodes each united to the outer terminal ofa pair of secondary coils 23 and 24 in series. The cathode of therectifier is heated by current from a secondary 25 and a secondary coil25a supplies current to the heaters of the cathodes of the tubes 6, 6aand 6'0, and the cathode filament of the tube 60 respectively. All ofthese secondaries are mounted upon the same iron core to be energizedfrom a primary 26 connected to a light or power circuit. From thejunction point of the coils 23 and 24 is led a conductor 27 which isgrounded through a resistance 28. The cathode of the rectifier 22 isconnected through a similar conductor and a coil 29 to the lead 33rimning to the conductor 21. The coil 29 may be the field coil of theloud speaker and may be in multiple with a condenser 30. Condensers 31may be shunted across the terminals of the coil 29 and resistance 28.The midpoint of secondary coils 23 and 24 is also joined by a conductor32 to the resistances 15 and 16 in series; and the lead 21 may begrounded through a pair of suitable resistances 35 and 36 in series. Thecommon terminal 14 of the screens for the plates of the tubes 6, 6a and6b is connected to a point between these resistances; and a branchconductor 34 connects the primary 19 to the coil 29.

This receiver operates in the well known man ner with its heater-typescreen-grid tubes and resistance-repeating arrangement of circuits. Whenthe band of longer wavelengths is to be employed, the coils of the tunedcircuits are all used with both sections active; and when the signalsare to be received on the band of shorter wavelengths, the sections 10,10a and 10?) are shorted out by bridging the two terminals of these coilsections. This result may be accomplished by suitable switching meanswhich will aiiect all three sections 10, 10a and 10b together, as willbe described later.

The receiver thus consists of two stages of radio-frequencyamplification followed by a detector; and this is succeeded by a singlestage of audio-frequency amplification employing a vacuum valve. Threetuned circuits provide for selectivity.

The radio frequency section is designed specifioally around a suitablescreen-grid valve. As the characteristics of this valve are such as toallow the plate circuit load to be developed across a high resistanceunit, which, in turn, is capacitycoupled to the tuned circuit, the useof only low plate-current valves is permitted. This circuit arrangementhas an advantage in that it allows the elements of the tuned circuits tobe connected directly to the frame of the receiver, and simplifiesconsiderably the radio-frequency filtering in the supply leads.

The performance of the receiver as regards sensitivity on both wavebands, selectivity on both wave bands, fidelity and power output, isquite satisfactory. The fidelity curve of the receiver illustrates anunusually good response over the audio range and is brought about byspecial circuit connections wherein the C bias resistor 15 of the powertube 60 is removed as an impedance common to the grid and platecircuits.

Reduction in loud speaker hum is brought about by the combination ofby-pass condensers 31 above described in the filter circuit, using thefield winding 29 of the loud speaker as the filter choke; tuning thisfield winding by means of a condenser 30 across its terminals,connecting the power tube grid circuits as shown, and a properpolarizing of the field winding and the primary 19 of the outputtransformer. A copper ring or slug may be placed adjacent to the fieldcoil in the loud speaker assembly to contribute to the speaker humreduction.

In practice we can obtain marked advantages with this receiver byadopting certain comparatively low values of the coupling resistances2a, 2b and 2c and the coupling condensers 5a, 5b and 5c.

Heretofore in resistance coupling between amplifiers in cascade thecoupling resistances have been of the order of 250,000 ohms or more andthe coupling condensers have had a value of .001 of a microfarad andover. With such values there was always difiiculty in obtaining wavelength range over the broadcast band with conventional variablecondensers and -coils.- Also there could be no control of the stage gainor amplification. This state of affairs is shown by reference to Figure4 which presents a chart having a curve showing the relation between therepeating resistance measured horizontally and the gain measuredvertically for a large value of a coupling resistance, and a condenserof comparatively large capacity. It will be seen that with largeresistance this curve flattens out and becomes horizontal and along thehorizontal portion the gain is constant and invariable. Only along thebend or diagonal part of this curve can control be obtained.

The essential reason for the limitation in the wave length range, whichcan be obtained with a coupling capacity of large value, is that thiscapacity, which is in series with the plate-cathode capacity of thetube, is shunted across the tuned circuit, associated with the inputcircuit of each of the tubes. Thus the gang condenser, that is to saythe assembly of tuning condensers, must be much larger than in ourinvention.

Further, large coupling resistances of 250,000 ohms, which are requiredwith large coupling condensers, cannot be used with vacuum amplifyingtubes of the type usually made in this country; and cannot be operatedwith anode supply voltages of reasonable amount, because the largeresistance wastes too much of the electrical energy which the anodecircuit receives. On the other hand, with a smaller coupling capacity,the practical value of the resistance may be very much reduced; as isdone in the practice of this invention; because the small couplingcapacity in series with the parallel tuned circuit constitutes animpedance of only a few thousand ohms. It is unnecessary to make thecoupling resistance any greater than this effective impedance of thecombined coupling condenser and tuned circuit. But

when a large coupling condenser is used, the effective value of theimpedance of the tuned circuit may be 200,000 ohms or more dependingupon the losses associated with the coil and condenser. Hence to obtaingood amplification, one must use both high coupling resistance and highanode voltage; which with tubes of the kind available in this country isimpractical. By means of relatively lower coupling resistance at smallercoupling capacities all of these difficulties are avoided.

We therefore give to these coupling resistances a value of the order of25,000 ohms and to the coupling condensers a value as low as 10micromicrofarads. Upon plotting a similar curve, as shown in Figure 5,one sees that for condensers of relatively low values the curve does notflatten out quite so abruptly, and that at low resistances the bend orslope of the curve can be utilized for working effect. Thus there iscase of obtaining wave length range and the stage gain or amplificationcan readily be controlled.

Obviously instead of two bands of wave lengths we can provide for morethan two by increasing the number of tuning coil sections; and severalbands can be obtained within any limits from the very high frequencyrange of 25 meters to the far lower frequency range of 25,000 meters.

In Figures 2 and 3 there is presented an actual construction showing howthe coils for the separate bands of wave lengths can be mounted andcontrolled in unison by actuating a single member which switches thecoil sections 10, 10a and 101) into or out of circuit. At 37 is a panelor support to which is attached three coils comprising the sections 9and 10, 9a and 10a, and 9b and 10b. The sections 9, 9a and 9b are woundon tubular forms 38; and other sections, which are indicated as toposition at 10, 10a and 10?), are wound on cylindrical forms 10; fixedon rods or pins 39 in the outer ends of the forms 38 and having theiraxes at right angles thereto. By spacing the various pairs of coilsections so that the axes of each pair of sections are at right anglesto each other, the coil sections have no inductive effect upon eachother. This is important because otherwise when the section 10, forexample, is short-circuited a large current would flow therein and adisturbance in function would result. The forms 39 are attached to thepanel 37 by angleshaped clips 40 and suitable screws and other fasteningdevices. Suitably affixed to the panel are annular projections 41concentric with the forms 38. These tubular projections havecircumferential ribs 42 which act as stops and 43 are caps or covers forthe various pairs of coil sections. The caps engage projections 41 bybeing slipped thereon until their ends abut the stops 42.

These caps or covers 43 for the coils also serve as electrostatic andelectromagnetic shields for the coils and confine all electrical effectsadjacent each coil to the space within the shield; thus preventingcondenser reactions between the groups of coils in the receiver.

The forms 38 have at their outer ends terminal clips 44 and 45 to whichconductors may be attached, so as to connect the ends of the coilsections into circuit. Each of these forms 38 also has a second pair ofterminal clips 44' and 45. One circuit wire may be connected to theterminal 44 of the section 9, for example, and another terminal wire mayunite the opposite terminal l5 of the section 9 with one terminal 44."of section 10. The other terminal 45' of section 10 may be connected tothe ground. Hence, if terminal 45 is grounded, the section 10 will beout of circuit.

To the face of the panel is attached a shelf 46 having its middleportion 47 bent up or raised. Near its opposite ends the shelf hasturned down side portions 48 and 49 with apertures to receive screws tosecure the shelf against the face of the panel 37. Adjacent the portion48 this shelf carries two casings 50, each of which contains a singlepclsingle throw toggle switch; having projecting terminals 51 and atoggle lever 52; the outer end of each lever 52 being cleft as shown. At53 is a switch red, one end of which is provided with fiat surfaces 54for a knob; and on this rod are rigidly mounted arms 55 which engage thecleft end of each lever 52 to enable these switches to be operated whenthe rod 53 is turned. A U-shaped member affixed to the bent up portion57 of the shelf 46 provides bearings for the rods 53.

In practice terminals 44 of each of the coils 10, 10a and 1% may each beconnected to one of the terminals 51 of one switch 50 and the terminal45' of each of these coils may be similarly connected to the remainingterminals 51 of one of the switches. Then when the rod or shaft 53 isturned, all of the switches 50 can be operated together to open circuitor short circhit the various coils 10, 10a and we as above described.

Of course, condensers 11, 11a, 111) will also be connected together inthe usual way, so that they can all be tuned in unison by means of asingle knob and shaft provided for this purpose.

The panel 37 may have ends or wings 58, one of which is perforated asindicated in Figure 3 to enable the rod 53 to project through it andcarry the operating knob on the outer side thereof.

By the use of resistance repeater coupling and capacity between variousstages, the simple switches shown at 50 are all that is needed to shiftfrom one wave length range to another. On the other hand, ifelectromagnetic coupling involving primary and secondary cells wereemployed, both the primary and secondary coils would have to be adjustedby increasing or decreasing the number of turns in each to maintain theproper coupling between each primary and secondary and thus complicatedswitching devices would become necessary. But, with resistance repeatercoupling such complicated switching devices can be dispensed with,because the resistance is just as effective at one wave len th as atanother.

Many changes in the details of the circuits and the construction shownand described herein may of course be made, and the invention is not tobe construed as limited to the precise form set forth, except asrequired by the express terms in which the appended claims are setforth.

Having described our invention, what we claim i. In a radio receiverhaving amplifying stages in cascade, tuning means for the input circuitsof each stage including asectional inductance comprising two coilsconnected in series, one coil being mounted in non-inductive relationinside the other of said coils, a tuning condenser connected acrosssectional inductance, and means for simultaneously short-circuiting allof said non-inductively mounted. coils.

2. In multistage amplifier having a plurality of tuned input circuits,means for altering the tuning range of said circuits, each of saidcircuits including a sectional inductance comprising two coils connectedin series, one coil being non-inductively mounted inside the remainingcoil, said means comprising a switch for simultaneously short-circuitingall of said non-inductively mounted coils.

3. A radio receiver comprising amplifying circuits in cascade, each ofsaid circuits having a tuning circuit connected thereto, said tuningcircuits comprising coils in sections, and means for short-circuitingone section of all the coils simultaneously, each of saidshert-circuited sections being in non-inductive relation to theremainder of the associated coil.

4. A receiver comprising radio frequency amplifying stages containingvacuum tubes in ciscade, each of said stages having a tuning circuit atits input side, said tuning circuit comprising a variable condenser anda coil in sections, and coupling means comprising a fixed resistance ofthe order of 25,600 ohms in the output circuit in each tube and acapacity of the order of 10 micromicrcfarads in the input circuit ofeach tube, and means for simultaneously short circuiting a section ofall of said coils.

LESLIE F. CURTIS. WILLIAM F. COTTER. LEONARD E. EASTMAN.

